Adhesive strength tester



y 1966 s. E. BLANCHARD ETAL 3,253,461

I ADHESIVE STRENGTH TESTER Filed May 4, 1962 SAMUEL E. BLANCHARD CLARENCE J. GARDNER. JR.

BY ROBERT CALVERT 23 ATTORNEY.

United States Patent 3,253,461 ADHESIVE STRENGTH TESTER Samuel Edson Blanchard, Decatur, Ill., and Clarence J. Gardner, Jr., Mount Upton, N.Y., assignors to The Borden Company, New York, N.Y., a corporation of New Jersey Filed May 4, 1962, Ser. No. 192,560 1 Claim. (Cl. 73-150) This invention relates to a machine for testing the tack and setting speed of adhesives with substantially no shearing effect.

The tester is of such accuracy as to distinguish the performance of different lots of adhesives that are similar in composition and Within the same manufacturing specifications. As a result, it is useful in such studies as the effect of minor differences in thickness of film, duration of time after the adhesive is applied to the surfaces to be bonded (dwell time), variation of an adhesive from lot to lot in tack or rate of development of strength in the film and selection of the adhesive for a given commercial use.

The invention provides a machine suitable for measuring the tack of an adhesive within a very short period of time such as 2 seconds or less after application with an accuracy to distinguish the differences produced by only minor variations in adhesive formulation.

The invention comprises the herein described means for pressing the surfaces to be bonded against an adhesive film therebetween and means for breaking the bond by applying a separative force applied in direction substantially perpendicular to the general plane of the film. In the commercial embodiment the machine includes means for holding the said surfaces in substantially parallel relationship to each other as they react to the separative force.

The invention is illustrated in the attached drawings.

FIG. 1 is a side elevation of the machine.

FIG. 2 is a view on an enlarged scale and partly in section of the portion of the machine holding in position the sheets of material to which the adhesive undergoing tests is applied.

FIG. 3 is a fragmentary view, partly in section, of the upper part of a support at the time of application of the adhesive.

The figures are in part diagrammatic and accessories not shown are conventional.

There are shown a supporting stand 10, an adherentholding table 12 mounted thereon and provided with plane upper surface, a rigid adherent-holding block member 14 thereabove with a plane lower face, and means for mounting the table and block movably towards and away from each other, with the said surface and face remaining generally parallel. The pivotal mountings 11, 13, 15, 17 and 19 in FIG. 1, to frames 38 and 39, cause continuing parallel alignment of the said surface and face as the said table and block are pulled apart against the tack of the adhesive film between the two members.

Means such as shown secure a sheet of paper 20 or the like over the surface of table 12 and a strip of the same or different material over the face of block 14. Thus double faced Scotch tape 23 holds the sheet to the table 12, and clamp 24 holds the strip over the block 14, the lower end of the clamp securing the paper in the grooves 29 provided in opposite sides of the rectangular block.

In the machine illustrated in FIGS. 1 and 2 the force which initially is used to press the adhesive-coated adherent on table 12 upwardly in the direction of the upper adherent covered block 14 is applied by any controlled conventional means, as by the piston 35 operated by air cylinder 28, with compressed air from line 31 with exit line 33. Clevis 36 attaches the piston 35 pivotally to one end of the power arm 34 wiah pivotal mounting 19. A bracket 32 mounts the air cylinder on the frame 38. The pivotal mountings 13 attaches the other end of the force arm to the support 12.

Means including the yoke 25, universal joint 11, and connecting rods 27 and 42 attach the block 14 to the spring scale 44 of conventional but highly sensitive type, with an indicating element and usual mechanism (not shown) causing the indicator to stop at the position of maximum pull thereon, which will be at the moment of failure of the adhesive. The pivotal mountings 11, 13 and 19 are disposed in each case with an axis transverse to the direction of length of the power arm, so as to cause the plane smooth faces of parts 12 and 14 to remain approximately parallel as these two members are pulled apart by slight downward movement of the right end of arm 34 (FIG. 1). This parallelism is promoted by the relatively long arm of the bar 34 and the parallelogram formed by points 19, 13, 15 and 17, so that a mini mum angular movement of the bar results when the faces of parts 12 and 14 are forced apart sufficiently to overcome the tack of the adhesive between ahe two sheets of paper or the like 20.

The brace 48 supports a guide 40 provided with an oversized slot through which the rod 42 moves, to accommodate the shifting required by the pivoting which occurs at 19, as stress on block 14 builds up by the extension of the spring scale 44 until adhesive failure occurs.

FIG. 3 shows the adhesive 59 applied in excess amount to the upper surface of the paper 20 as the hand operated wire wound doctor rod 52 is forced down upon the surface of the paper and drawn, with a bank of adhesive ahead if it, in non-rotating manner across and over the paper surface so as to apply a controlled thickness of adhesive film to the paper.

In this machine shown in FIGS. 1 and 2 timing is effected manually, by use of a usual foot switch (not shown) which is depressed immediately after the adherent is coated (or at the end of any desired open period). This foot switch also starts an electrical timer at the moment it is depressed. At the end of the desired closed time as determined by watching the sweep second hand on this timer, the foot switch is raised, stopping the timer and opening the adhesive bond. The exact time can then be read on the dial of the timer and the load required to open the bond read on the dial of the spring scale.

Materials of construction are those that are usual in test machines of this type as, for example, stainless steel, brass, aluminum and various alloys. Hard rubber also is suitable for the face of block 14. The pulling spring 44 is constructed of spring steel. The adhesive of the Scotch tape and also the paper, textile, or other sheet material to which the glue to be applied, must have strengths greater than the tack of the glue to be tested. The pivotal mounting 11 includes conventional elements (see FIG. 1) causing the parts below the joint to be angularly displaceable, in at least each of two planes at a right angle to each other. A solenoid of usual kind and with usual connections (not shown) may be substi- 3 tuted for the pneumatic means for causing the travel of table 12.

Dimensions also are usual and not critical. Representative ones are an overall length of about inches for the power arm 34; 1 inch square for the plane, downward face of block 14; and 4 x 4 inches for the plane, upper face of the support 12. The movement required of block 14 and support 12 to actuate the force measuring device should be as short as possible. In the case of the model shown in FIGS. 1 and 2, this will be less than /2 inch.

The operation of the machine will be largely evident from the description that has been given. The sheet of paper or other material used is wettable by the adhesive. A strip of width approximately equal to the width of the support selected, i.e., 12, is adhered over the plane surface, the adherence being effected by the double face Scotch tape 23 having pressure sensitive adhesive on both sides thereof. The adhesive on the Scotch tape is of strength greater than the adhesive strength of the adhesive to be tested. Adhesive 50 in excess amount is then poured at one end of the upper surface of the sheet on an area not to be later contacted by block 14. The adhesive is then drawn across the test area by pressing the doctor rod across the paper, so as to spread the adhesive over all the face of the paper in a film that levels to substantially uniform thickness. The thus coated paper is exposed to the atmosphere for any precontact is desired. One of the advantages of this instruselected open drying period. Normally, immediate contact is desired. One of the advantages of this instrument is the ability to reduce this open time to a very small fraction of a second.

Another strip of the paper 22 or other desired adherent of width equal to the length of the edge of the square face of the block 14, will in the meantime have been drawn taut over the face of this block and the ends folded up so they extend above the level of the grooves 29. The clamps 24 are then inserted in position, so that the lower flanged ends thereof extend into the grooves, force the paper ahead of them and secure the paper in the grooves. Spring 45, held in a conventional manner to and under tension between the clamps 24, draw the points of the clamps tightly against the paper or other sheet material extending over the grooves 29 (see FIG. 4). At the conclusion of the open period, the compressed air is admitted through line 31 of FIG. 1 so as to force the block 14 and the support 12 to press firmly the intervening layer of adhesive 50. Pressure consolidation is then continued for the preselected dwell time.

At the end of the dwell time the direction of the air fiow in the air cylinder 28 is automatically or manually reversed, so that the force is now separative and tends to pull the block 14 and the support 12 apart. In the construction shown in FIGS. 1 and 2, for instance, this separative force acts through the force arm 34. The pivotal mounting of the arm 34 and parts associated therewith maintain the plane of the face of the support 12 so that it is kept in substantially parallel alignment with the surface of the block 14. This prevents initiating separation at an edge of the assembly by tilting of the support.

Control of the rate of admission of air is obtained in the instrument illustrated in FIGS. 1 and 2 by controlling the rate of air flow through line 33 by micrometer diaphragm valve.

The flow of air is continued, after the reversal until the tack of the adhesive is overcome and the separation of the test surfaces is completed. The indicator will read the maximum force required to overcome the tack of the adhesive. The adhesive and the paper to which it is applied are then removed, new strips of paper and a new application of adhesive are used and the test is repeated as before.

The results read on the indicating gauges or dials as tack failure are recorded and used to calculate the force at such failure in terms of pounds per square inch of the adhesive film undergoing test.

The sensitiveness of the apparatus is illustrated by the following results of two series of tests on polyvinyl acetate emulsions of somewhat different types, both of which are within the specifications for this product, have the same solids content, have viscosities within the range 900-1200 cps. on a Brookfield viscosimeter, and are of pH 4.0-5.0. All separations were effected by the pulling force directed at a right angle to the plane of the film of adhesive under test, this particular data being obtained with the tester of FIGS. 1 and 2 with essentially zero second open time.

Pull at Separation, p.s.i. Dwell Time (Press Closed) In another test, the results for three more polyvinyl acetate emulsions, all submitted for use in side seams of corrugated shipping cases, are shown below and will illustrate the reproducibility of results obtainable on this instrument. Each value in this table represents a single test reading.

Pull, p.s.i., for Various Dwell Timcs'Triplicule Tests Adhesive No.

I 2 Sec. Dwell 5 Sec. Dwell 10 Sec. Dwell 1. l0 1. 5. 0 0. 9O 1. (i5 5. 0 0. 85 l. 50 5. 0 0. 90 l. 3 1. 9 0. 85 1. 2 1. 95 0. 1. 35 2. 00 70 1. 45 2. 20 1. 35 2. 40 1. 65 2. 50

The maximum variation of any value from the average, in a total of 9 series of tests is only 0.17.

It will be understood that it is intended to cover all changes and modifications of the examples of the invention herein chosen for the purpose of illustration which do not constitute departures from the spirit and scope of the invention.

We claim:

A testing machine for measuring the tack of an adhesive film between parallel, plane faces of two movable rigid members which machine comprises:

(1) means for securing a sheet of adhesive wettable material to each of the plane faces of said movable rigid members;

(2) means for pressing an adhesive film between said sheets for a predetermined period of time;

(3) means for pulling said plane faces of said movable rigid members away from each other subsequent to the elapse of said predetermined period of time, in direction perpendicular to said faces until the adhesive fails;

(4) means for indicating the magnitude of the force required tocause said failure; and

(5) measuring means for measuring the force required to cause said failure comprising a spring secured to one of said movable rigid members and to said indicating means which spring expands under 5 6 tension by the action of the other of said movable References Cited by the Examiner rigid members being pulled away from said first UNITED STATES PATENTS mentioned member, said expansion being caused by the pull of said second mentioned member being gg 7 transmitted through said adhesive film to said first 5 2773482 12/1956 s i g X Pemloned member PY P Sald first P 3,129,586 4/1964 Allen et a1 73-150 x tioned member to move initlally 1n the same direction with second mentioned member and which RICHARD QUEISSER Primary Examiner spring contracts after failure of said adhesive film thereby causing said first mentioned member to 10 JOSEPH STRIZAK Examiner move away from said second mentioned member. L. MOK, J. 1. SMITH, Assistant Examiners. 

